Metal Ion Beams Research Articles

Power Supply System for Vacuum-Arc Ion Source With Millisecond Pulse Length

This article deals with a vacuum-arc ion source, which generates high-intensity beams of metal ions. The power supply system largely determines the ion source parameters such as accelerating voltage, average current, and pulse current densities of the ion beam. This article proposes the power supply system for the vacuum-arc ion source intended for the generation of pulses with the length up to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2000~\mu \text{s}$ </tex-math></inline-formula> at an accelerating voltage up to 50 kV. At the frequency of 50 Hz, the average ion current can reach 50 mA due to long pulses. This article considers the main design solutions for the generation of long pulses. A comparison is given to the novel power supply system based on insulated-gate bipolar transistors (IGBTs) and the earlier thyristor power supply.

Requirements for Designing an Effective Metallic Nanoparticle (NP)-Boosted Radiation Therapy (RT).

Simple SummaryRecent advances in nanotechnology gave rise to trials with various types of metallic nanoparticles (NPs) to enhance the radiosensitization of cancer cells while reducing or maintaining the normal tissue complication probability during radiation therapy. This work reviews the physical and chemical mechanisms leading to the enhancement of ionizing radiation’s detrimental effects on cells and tissues, as well as the plethora of experimental procedures to study these effects of the so-called “NPs’ radiosensitization”. The paper presents the need to a better understanding of all the phases of actions before applying metallic-based NPs in clinical practice to improve the effect of IR therapy. More physical and biological experiments especially in vivo must be performed and simulation Monte Carlo or mathematical codes based on more accurate models for all phases must be developed.Many different tumor-targeted strategies are under development worldwide to limit the side effects and improve the effectiveness of cancer therapies. One promising method is to enhance the radiosensitization of the cancer cells while reducing or maintaining the normal tissue complication probability during radiation therapy using metallic nanoparticles (NPs). Radiotherapy with MV photons is more commonly available and applied in cancer clinics than high LET particle radiotherapy, so the addition of high-Z NPs has the potential to further increase the efficacy of photon radiotherapy in terms of NP radiosensitization. Generally, when using X-rays, mainly the inner electron shells are ionized, which creates cascades of both low and high energy Auger electrons. When using high LET particles, mainly the outer shells are ionized, which give electrons with lower energies than when using X-rays. The amount of the produced low energy electrons is higher when exposing NPs to heavy charged particles than when exposing them to X-rays. Since ions traverse the material along tracks, and therefore give rise to a much more inhomogeneous dose distributions than X-rays, there might be a need to introduce a higher number of NPs when using ions compared to when using X-rays to create enough primary and secondary electrons to get the desired dose escalations. This raises the questions of toxicity. This paper provides a review of the fundamental processes controlling the outcome of metallic NP-boosted photon beam and ion beam radiation therapy and presents some experimental procedures to study the biological effects of NPs’ radiosensitization. The overview shows the need for more systematic studies of the behavior of NPs when exposed to different kinds of ionizing radiation before applying metallic-based NPs in clinical practice to improve the effect of IR therapy.

Production of metallic ion beams by electron cyclotron resonance ion sources equipped with inductive heating ovens at the Institute of Modern Physics.

A high-temperature oven based on the inductive heating technology was developed successfully at the Institute of Modern Physics in 2019. This oven features a durable operation temperature of over 2000 °C inside the tantalum susceptor. By carefully designing the oven structure, the material compatibility issue at high temperature has been successfully solved, which enables the production and routine operation of refractory metal ions with SECRAL-II (Superconducting Electron Cyclotron Resonance ion source with Advanced design in Lanzhou No. 2). To further apply this type of oven to the room temperature ECR ion sources LECR4 and LECR5 (Lanzhou Electron Cyclotron Resonance ion source No. 4 and 5), a mini-inductive heating oven has been fabricated and tested in 2020. By directly evaporating calcium oxide, some high charge state calcium beams have been produced successfully, such as 52 euA of 40Ca16+, 30 euA of 40Ca17+, and 12 euA of 40Ca18+. The detailed design and testing results will be presented and discussed.

Formation, Focusing and Transport of Highintensity, Low-Energy Metal Ion Beams

High-intensity implantation of low-energy ions into various materials demonstrates the formation of long, ionalloyed layers having a thickness of tens and hundreds of micrometers. A deep incorporation of alloying elements in materials is achieved, first of all, due to a stronger radiation-induced ion diffusion at ultrahigh current densities and radiation fluence ranging from 1020 to 1022 cm2, when the diffusion coefficient exceeds its classical value derived from Arrhenius theory by several orders of magnitude. Nevertheless, the generation of low-energy ions with energies of several or a few kiloelectronvolts at high current densities of several hundreds of milliamperes per square metre and their effective transport, is a sophisticated problem. The paper studies the ballistic focusing of high-intensity pulsed ion beams at 2 kV accelerating voltage, 800 μs pulse time, 0.8 duty cycle, and their propagation through the preliminary injected low-density background plasma.

Ti+ and Mg+ Ion Beam Extraction from the Modified Bernas Ion Source

The korea multi-purpose accelerator complex (KOMAC) has a metal-ion-beam irradiation facility (150 keV/1 mA) equipped with a Bernas ion source. Metal-ion beams such as Cr+, Fe+, Co+, and Cu+ have been successfully extracted from our facility. Recently, some research groups have requested us to irradiate Ti+ and Mg+ ions into materials. These two kinds of ions have never been provided before. In response to these requests, we carried out the extraction of Ti+ and Mg+ beams at our facility. The vaporization temperatures of TiCl(III) and MgCl(II) under a pressure of 10−4 Torr were less than 300 °C and more than 600 °C, respectively. In this study, optimal extraction conditions for Ti+ and Mg+ ion beams were acquired successfully. To confirm the fluences of the Ti+ and the Mg+ beams, we prepared a silicon wafer sample and a gallium nitride (GaN) sample. Ti+ ions were irradiated with a current density of ∼6 μA/cm2 onto a silicon wafer sample for 90 min, and the dose was 1.68 × 1016 ions/cm2, we measured by using Rutherford backscattering spectrometry (RBS) analysis. Mg+ ions implanted in GaN were confirmed by using secondary ion mass spectroscopy (SIMS). The depth and the concentration of Mg+ ions at the peak were found to be 130 nm and 7.4 × 1019 ions/cm3, respectively. We would expect the newly extracted Ti+ and Mg+ ions to be helpful for research in the fields of material science and condensed matter physics.

Production of Intense Ion Beams of Nickel, Chromium, Silicon, and Cobalt at the DC-60 Cyclotron

This article describes experiments for producing highly intense metal ion beams at the ECR source of the DC-60 cyclotron using the evaporation of organometallic compounds by the MIVOC method. As a result of the works, beams of nickel, cobalt, chromium, and silicon ions are obtained. The optimization of modes of acceleration for the ion beams to an energy of 1.75 MeV/n is carried out.

Formation of high-intensity axially symmetric and ribbon beams of low-energy metal ions.

Low-energy metal ion beams are of considerable interest in developing a high-intensity implantation method that modifies the elemental composition, microstructure, and properties of various materials at depths many times exceeding the projective range of ions. This study presents the results of experiments on plasma-immersion formation followed by spherical and cylindrical ballistic focusing of aluminum and titanium ion beams. The features of the formation, transport, and ballistic focusing of an ion beam are discussed based on the parameters of the vacuum-arc plasma, conditions of its preliminary injection into the drift space and beam focusing, amplitude, duration, and frequency of the bias potential pulses. The optimal conditions to form high-intensity beams of metal ions purified from the macroparticle debris of a vacuum-arc with a current of higher than 1 A and a current density of up to 0.5 A/cm2 are determined.

Development of a new high temperature oven for the production of intense metal ion beams with ECR ion sources.

High Temperature Ovens (HTOs) have widely been used to evaporate refractory materials in electron cyclotron resonance ion sources to produce hundreds of microamperes of multiply and highly charged metal ion beams. To meet the demands of milliamperes of multiply charged uranium and other heavy metal ion beams for future accelerators, a new and low-cost HTO is under development at Lawrence Berkeley National Laboratory for better long-term stability at high evaporation rates. ANSYS simulations have been carried out to optimize the new HTO with low heating current to reduce the electromagnetic forces as an HTO is immersed in the strong ECRIS magnetic fields. A larger loading volume is employed to deal with higher material consumption. Off-line tests have shown that the unloaded new HTO operates stably up to 1800-1900 °C with low temperature gradients and good repeatability. This paper presents and discusses the conceptual design features of the new HTO and off-line tests.

Optical spectroscopy as a diagnostic tool for metal ion beam production with an ECRIS.

At GSI, the CAPRICE ECRIS is used to provide heavy ion beams to the UNILAC (Universal Linear Accelerator) accelerator. In order to satisfy the demand of metal ion beams, a resistively heated oven is routinely used. This evaporation technique allows the ion beam production from natural and enriched solid elements or compounds with high efficiency and low material consumption. Often it is required to provide high charge state ion beams from rare or extremely rare isotopes as 48Ca, e.g., for the investigation of super heavy elements. In order to maintain the ion beam stable for the entire scheduled beam time, the plasma inside the ion source must remain as stable as possible. The tuning of ion source parameters and oven power affecting the oven temperature and, in turn, the evaporation rate is necessary. A strong relationship between the microwave power and the oven heating was observed, thus affecting the power control, the plasma stability, and the material consumption. Hence, it was investigated how an optical spectrometer can be used as a predictive diagnostic tool to detect ion source instabilities. Furthermore, the effect of parasitic oven heating by coupling of microwaves was investigated. Optical emission spectroscopy was performed by analyzing the light from the plasma and from the oven through the extraction aperture. The measurements enabled us to distinguish between resistive heating and microwave heating. The results of this investigation are presented.

Modeling Transport in a System with Ballistic Focusing of a High Intensity Beam of Metal Ions

Major patterns of ion beam transport in a system with ballistic focusing are studied via numerical modeling. It is shown that the efficiency of transporting a beam of metal ions at 0.66 A and an ion energy of 1–3 keV depends on the voltage bias and plasma density in the beam’s drift space. Incomplete compensation for high-speed ions in the beam transport channel lowers the potential and (under certain conditions) produces a virtual anode. The ion-electron emission of electrons from targets and grid electrodes is an additional mechanism of compensating for the spatial charge of a beam of metal ions.

Temperature gradients in targets with high-intensity implantation and their influence on the characteristics of ion-modified layers

This paper is devoted to the study of the gradient temperature field dynamics and distribution in the metal targets irradiated with high-intensity beams of gas and metal ions. The investigations concerned ion implantation modes with the ion beam current density from several tens of mA·cm−2 up to A·cm−2 were investigated. The ion beam power was additionally varied due to the change of ion energy in the range from 0.6 to several keV and the pulse duty factor in the range of 0.2–0.8. The integral temperature of the target was measured with an electrically isolated thermocouple. To measure the dynamic change in the local temperature on the irradiated target a high-temperature pulse pyrometer KLEIBER 740-LO was used. The problem of temperature evolution and metal sample melting under the exposure of a high-intensity repetitively pulsed ion beam was solved numerically using the heat conduction equation written in cylindrical coordinates. Analysis of the experimental data obtained with the use of electrically isolated thermocouple, pulse pyrometer, and numerical simulation revealed the presence of significant gradient temperature fields both over the surface and along the depth of targets irradiated by high-intensity ion beams.

Laser ablation plasma with solenoid field confinement.

A Laser Ion Source (LIS) can produce high charge state and high intensity ion beams (∼emA), especially, refractory metallic ion beams, which makes it a promising candidate as an ion source for heavy ion cancer therapy facilities and future accelerator complexes, where pulsed high intensity and high charged heavy ion beams are required. However, it is difficult for the LIS to obtain a long pulse width while ensuring high current intensity, thus limiting the application of the LIS. To solve the conflict, magnetic fields are proposed to confine the expansion of the laser produced plasma. With a solenoid along the normal direction to the target surface, the lateral adiabatic expansion of the laser ablation plasma is suppressed which extends the pulse width of the ion beam effectively. The characteristics of laser ablation plasma with solenoid field confinement will be presented and discussed in this paper.

Xe Plasma vs. Gallium FIB Delayering

Abstract Liquid metal ion and plasma beam FIB systems are widely used in the semiconductor industry for TEM lamella preparation, circuit edit, and cross-sectional analysis. This article compares the deprocessing capability of a Ga FIB with that of a Xe plasma FIB. Both systems were used to delayer an Intel 14 nm processor from M8 down to the transistor contacts. As the images in the article show, a 100 × 100 µm window was opened by the Xe plasma FIB and a 20 × 20 µm window was opened with the Ga FIB. Related issues such as processing time, end point detection, and surface roughness are also discussed.

New exotic beams from the SPIRAL 1 upgrade

Since 2001, the SPIRAL 1 facility has been one of the pioneering facilities in ISOL techniques for re-accelerating radioactive ion beams: the fragmentation of the heavy ion beams of GANIL on graphite targets and subsequent ionization in the Nanogan ECR ion source has permitted to deliver beams of gaseous elements (He, N, O, F, Ne, Ar, Kr) to numerous experiments. Thanks to the CIME cyclotron, energies up to 20 AMeV could be obtained. In 2014, the facility was stopped to undertake a major upgrade, with the aim to extend the production capabilities of SPIRAL 1 to a number of new elements. This upgrade, which is presently under commissioning, consists in the integration of an ECR booster in the SPIRAL 1 beam line to charge breed the beam of different 1+ sources. A FEBIAD source (the so-called VADIS from ISOLDE) was chosen to be the future workhorse for producing many metallic ion beams. This source was coupled to the SPIRAL 1 graphite targets and tested on-line with different beams at GANIL. The charge breeder is an upgraded version of the Phoenix booster which was previously tested in ISOLDE. It was recently commissioned at LPSC and lately in the SPIRAL 1 beam lines with stable beams. The upgrade additionally permits the use of other target material than graphite. In particular, the use of fragmentation targets will permit to produce higher intensities than from projectile fragmentation, and thin targets of high Z will be used for producing beams by fusion-evaporation. The performances of the aforementioned ingredients of the upgrade (targets, 1+ source and charge breeder) have been and are still being optimized in the frame of different European projects (EMILIE, ENSAR and ENSAR2). The upgraded SPIRAL 1 facility will provide soon its first new beams for physics and further beam development are undertaken to prepare for the next AGATA campaign. The results obtained during the on-line commissioning period permit to evaluate intensities for new beams from the upgraded facility. © 2001 Elsevier Science. All rights reserved.

Investigation of structural and magnetic properties of Co+ ion implanted indium tin oxide thin films on polyethylene terephthalate (C10H8O4)n substrates by 100 keV ions

Indium Tin Oxide (ITO) thin films have been used extensively in many applications, such as solar cells. In particular, ITO has been the material of choice in flat panel displays as one of its electrodes due to its low resistivity, high transmission of visible light and high free carrier density that contributes to its relatively low electrical resistivity. Modification of ITO thin films on polymer substrates using transition metal ion beams is rarely reported in literature. In this work, ITO thin film samples were implanted with Co+ ions of energy 100 keV at fluences 1 × 1014, 1 × 1015 and 1 × 1016 ions/cm2. The grain sizes of the ITO thin films were observed to increase with increase in ion fluence, showing that the quality of the ITO thin films and crystallinity were getting enhanced. At a fluence of 1 × 1016 ions/cm2, a high value of 2.33 × 10−3 emu/g magnetization was estimated. The level of residual magnetism in the Co+ implanted thin films increased at an average of 35% with increase in ion fluence. This means that Co+ implanted ITO thin films have good ability to retain a certain amount of residual magnetic field at zero magnetizing, as the ion fluence increases. Furthermore, the Co+ ion implanted ITO thin films were found to exhibit clear room temperature ferromagnetism. The shift in hysteresis loops along applied magnetic field axes provides information about the exchange bias of Co+ ion implanted ITO thin films in relation to grain size.

Studies of the Electrochemical Properties of Thin-Film Materials for Coating Cardiac Stimulator Electrodes

The frequency characteristics of the admittances of a series of candidate materials for coating pacemaker electrode poles were studied. A method for assessing the properties of current transfer from an electrode connected to a source of stimulatory impulses to tissues is described. The main factors influencing decreases in the effectiveness of this transfer are identified. Potential physical vapor deposition technologies for depositing coatings, followed by alloying of films with metal ion beams, which increase the production of charged particles on the surfaces of the poles, are presented.

Redesign of the GANIL GTS ECRIS for 1+/n+ studies

More than half of the beams produced at GANIL are metallic elements, underlining the importance of their continuing development. Compared to the conventional techniques (oven, sputtering, MIVOC), the 1+/n+ method has demonstrated superior ionization efficiencies, suggesting the potential for improved metal beam production. Dedicated studies are required to assess the feasibility of this approach. The SPIRAL1 Charge Breeder is now in operation at the GANIL radioactive beam facility SPIRAL1. Operation in high radiation area poses challenges for its future development. A separate test stand supporting charge breeder and metal ion beam R&D is thus desirable.The GTS 14.5 GHz ECRIS has been chosen as a platform for 1+/n+ studies. After the upgrade program of 2017–2018, the GTS provides good performance and versatility, making it well-suited for ion source R&D. A new injection module has been designed for 1+ injection into the GTS plasma to be used in the 1+/n+ studies. It can be easily replaced with the conventional system for normal ion source operation. The design of the new injection system will be presented in detail with ion optical simulations of the 1+ beam injection.

Numerical simulation of high-intensity metal ion beam generation

The features and regularities of plasma-immersion formation of high-intensity repetitively pulsed beams of aluminum ions, as well as their transportation and ballistic focusing in an accelerating system with a curvilinear extracting potential grid electrode under application of negative bias with high pulse repetition rate of f = 105 Hz are studied by numerical methods. It is shown that the amplitude and shape of the ion beam current pulse depend significantly on the dynamic conditions of space charge neutralization of the beam. In case of using of bias potential with high duty factor, e.g. conditions of limited time of vacuum-arc plasma preinjection, the process of transportation and ballistic focusing of the ion beam up to densities manifold exceeding the density of the preliminary injected plasma, it is possible to obtain conditions leading to the formation of a virtual anode. It is shown that secondary electrons can be one of the additional mechanisms of compensation of the beam space charge which results in the improvement of transportation of high-intensity beams of aluminum ions.

METAL ION BEAMS PRODUCTION AT ECR-SOURCE “DECRIS-3” WITH SOLID STATES HEATING TECHNIQUE

Accelerated beams of metal ions are required for a series of scientific and technical tasks in the field of radiation physics of a solid state, for example, the only method for rapid assessments of the radiation damage investigation, the developed structural materials of nuclear technology is ion irradiation. The standard methods for production ion beams at ECR-sources from gas mixtures cannot fully meet the requirements of the experiment. To increase the spectrum of accelerated ions at the cyclotron DC-60 is working on developing methods of heating the solid substances to produce multiply charged ion beams of metals into an ECR ion source DECRIS-3. The article is dedicated to description of methods of production ion beams of metals in two ways: the direct injection of a substance into plasma and a method of heating the crucible with a working substance by micro-furnace. As a result of the work carried out on the DC-60 cyclotron, beams of lithium ions 6,7Li, 24Mg magnesium, 31P phosphorus and 40Са calcium were produced for the first time. Using these methods was produced beams of lithium ions 7Li1+ metal consumption of 1.1 mg/hour and derived a ion beam current of 500 µA, magnesium 24Mg4+ with the consumption of the substance 2.1 mg/hour and intensity of 81 µA, phosphorus consumption of substances 1.7 mg/hour at the beam current 31P5+ 60 µA and calcium 40Ca5+ with the consumption of a substance of 0.7 mg/hour when the beam current is 140 µA.

High intensity, macroparticle-free, aluminum ion beam formation

We describe a vacuum arc based system for the generation of repetitively pulsed metal ion beams with very high current density, and the results of experimental investigations of the performance of this new system, as well as the results of numerical simulations. Our approach uses a DC vacuum arc as a metal plasma source, and the beam-forming technique is a hybrid method using features of conventional gridded ion extraction together with some plasma immersion attributes. A hemispherical grid is located some distance from the plasma source so as to intercept part of the metal plasma flow and repetitively pulse-biased to the requisite ion beam energy. Ions are accelerated in the high voltage sheath that forms in front of the biased grid and focused into a converging beam that can be of a very high current density. Space charge neutralization is provided by cold plasma that streams through the grid during the bias-off part of the cycle. At the same time, macroparticles in the vacuum arc plasma are blocked from viewing the target by a metal disk positioned centrally on the hemispherical grid. In the work outlined here, we formed 5 keV aluminum ion beams with a current density up to 470 mA/cm2 at a negative bias amplitude of 3 kV and a pulse repetition rate of 105 pulse per second. The experiments and numerical simulations demonstrate the formation of high-intensity macroparticle-free aluminum ion beams for material surface modification and other possible applications.